The invention relates to a device for decurling flat printing materials, in particular, printed sheets, for a machine for processing the printing materials, in particular, a sheet-processing rotary printing machine having a guide surface section formed with a decurling notch over which the printing materials are drawn, suction openings arranged along and in the decurling notch and penetrating the guide surface section, an evacuation system fluidically connected to the suction openings, and also a machine equipped with the evacuation system and serving for processing flat printing materials, in particular, a sheet-processing rotary printing machine.
A device of the foregoing general type is disclosed, for example, by the published German Patent Document DE 26 29 421 C2. The suction openings of this heretoforeknown device have, for each 30 cm length of the decurling notch, a total cross section lying within a range between only 0.3 and 1.0 cm2. Relatively low leakage is, in fact, attained therewith in the case wherein the printing materials to be decurled do not cover all of the suction openings due to the format of the printing materials, a most extensive planar shaping of the printing materials by smoothing the printing materials being unachievable with this conventional device, in particular when the printing materials, due to corresponding printing thereof, exhibit successive regions along the decurling notch with considerable differences in ink layer thickness and when, in the case of particular print jobs, for example, an area printed over the entire surface and possibly with a great ink layer thickness is followed by an unprinted area. Trouble-free further processing of printed sheets, for example in the form of operations such as cutting, punching, folding, stapling and so forth, demands that the form of the printing materials be as planar or flat as possible, however.
It is an object of the invention to provide a device for decurling flat printing products, which are created by a rotary printing machine for processing flat printing materials, for trouble-free further processing. In this regard, it is an object of the invention to provide a device of the general type mentioned at the introduction hereto wherein, after the printing materials have passed the decurling notch, they have the flattest possible form, independent of subject-induced conditions. With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for decurling flat printing materials for a machine for processing the printing materials, comprising a guide surface section whereover the printing materials are drawable, the guide surface section being formed with a decurling notch, and with suction openings arranged along and in the decurling notch and penetrating the guide surface section, and an evacuation system fluidically connected to the suction openings, the suction openings being formed in successive groups thereof, and the evacuation system including a plurality of chambers, of which respective chambers are assigned to a respective one of the groups of suction openings, the chambers being selectively settable with equal and unequal negative pressures therein during operation.
In accordance with another feature of the invention, a vacuum generator is assigned to each of the chambers, the vacuum generator having a controllable gradient.
In accordance with a further feature of the invention, the chambers include a central chamber and an outer chamber on each side thereof, mutually adjacent chambers of said central and said outer chambers being connected to one another via a throttle, the decurling device further comprising a vacuum generator connected to said central chamber, and controllable valves, respectively, via which each of said outer chambers is connected to atmosphere.
In accordance with an added feature of the invention, the vacuum generator has a controllable vacuum gradient.
In accordance with an additional feature of the invention, the central chamber connected to the vacuum generator is also connected to a bypass open to the atmosphere and having one of the controllable valves inserted therein.
In accordance with yet another feature of the invention, a respective one of the chambers is connected via a throttle to a vacuum generator common to the chambers and, respectively, to a bypass open to atmosphere, a respective controllable valve being inserted into the respective bypass.
In accordance with yet a further feature of the invention, the printing materials are printed sheets, and the machine for processing the printing materials is a sheet-processing rotary printing machine.
In accordance with a concomitant aspect of the invention, there is provided a machine for processing flat printing materials having a device for decurling flat printing materials in the machine, comprising a guide surface section whereover the printing materials are drawable, the guide surface section being formed with a decurling notch, and with suction openings arranged along and in the decurling notch and penetrating the guide surface section, and an evacuation system fluidically connected to the suction openings, the suction openings being formed in successive groups thereof, and the evacuation system including a plurality of chambers, of which respective chambers are assigned to a respective one of the groups of suction openings, the chambers being selectively settable with equal and unequal negative pressures therein during operation.
Thus, in order to achieve the object of the invention, provision is made for the suction openings to form successive groups, and for the evacuation system to comprise a plurality of chambers, of which a respective chamber is assigned to a respective one of the groups of suction openings, and for equal or unequal negative pressures to be selectively or optionally settable in the chambers.
With this construction, printing material passing the decurling notch can be deformed differently zonally, and it is possible to refrain zonally from any deformation, a respective zone having an extent along the decurling notch which corresponds at least approximately to the corresponding extent of a respective group of suction openings.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for decurling flat printing materials, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: